Particularly in wind power plants, transmissions are used for transforming the torque and rotational speed between the transmission input and transmission output shafts, In this context a high torque applied to the transmission input shaft with a low rotational speed is converted to a lower torque applied to the transmission output shaft with a higher rotational speed. Basically, these transmissions can be divided into transmission types that comprise either planetary stages connected in series one behind another or planetary stages that are connected in parallel. The latter category includes the so-termed differential transmission which as a rule consists of three planetary stages. By virtue of suitable coupling of the first two planetary stages, a suitable torque distribution between the two planetary stages can be obtained. The summation in the third planetary stage allows the power to be recombined and correspondingly, along with that, a large transmission ratio range to be obtained.
A transmission of this type for wind power plants is known from EP 1 240 443 B1. It consists of a symmetrically configured planetary stage on the drive input side, downstream from which is connected at least one transmission stage, wherein the planetary stage consists of at least two equally dimensioned, power-dividing planetary gear systems connected in parallel. Downstream from the power-dividing planetary gear systems is connected a load-equalizing differential transmission stage. The differential transmission stage is designed as a passive differential in the form of an equalizing planetary gear system. It affects uniform power branching to the two connected sun shafts of the planetary stages that consist of the planetary gear systems. In this case one sun shaft is functionally connected to the sun gear and the other sun shaft to the ring gear of the differential transmission stage, whereas the planetary carrier of the differential transmission stage forms the drive output. Alternatively, the differential transmission stage is designed as an active differential in the form of an axially soft-mounted equalizing spur gear pair with opposite helical gearing. On the one hand this produces a uniform power distribution between the two connected sun shafts of the planetary stages consisting of the planetary gear systems, and on the other hand it is involved as a transmission stage in the overall transmission ratio of the transmission. In this case one sun shaft is functionally connected to one of the equalizing spur gears of the equalizing spur gear pair and the other sun shaft is functionally connected to the other equalizing spur gear.
Furthermore, WO 2008/104258 A1 describes a transmission for a wind power plant, which comprises a rotor shaft having, in an inside space, a first planetary stage and a second planetary stage of a planetary gear system. Relative to a longitudinal axis, the first planetary stage and the second planetary stage are arranged in series. The rotor shaft is coupled in a rotationally fixed manner to the planetary carrier of the first planetary stage and to the ring gear of the second planetary stage. The planetary gearwheels of the second planetary stage are fixed to the housing. A ring gear of the first planetary stage and a sun gear of the second planetary stage form a unit that rotates as one piece. Radially inside, a torque support piece a third planetary stage is integrated in an aperture located radially around the longitudinal axis. Third planetary gearwheels are mounted on a radially outward-facing connection ring of an inner coupling shaft, on third planetary carrier bolts positioned there. A central shaft serves as the third sun gear. The third planetary stage transmits the overall power with a very high rotational speed.